Material surface modification using friction stir welding hybrid process

ABSTRACT

A system and method for modifying a work piece surface of high melting temperature materials such as Advanced High Strength Steels, wherein a friction stir welding tool may include cutting elements located on the outside diameter of a collar assembly, wherein the collar assembly may be retrofitted for existing friction stir welding tools, or may be designed as a custom attachment for a new hybrid friction stir welding tool, wherein the surface of the work piece may be modified by removing detrimental flash and burr created during operation of the friction stir welding tool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/623,710, filed Sep. 20, 2012, which claims the benefit of andpriority to U.S. Provisional Patent Application No. 61/536,959, filedSep. 20, 2011, the entireties of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field Of the Invention

This invention relates generally to friction stir welding (FSW) and itsvariations including but not limited to friction stir processing (FSP),friction stir spot welding (FSSW), friction stir spot joining (FSSJ),friction bit joining (FBJ), friction stir fabrication (FSF) and frictionstir mixing (FSM) (and hereinafter referred to collectively as “frictionstir welding”).

2. Description of Related Art

Friction stir welding is a technology that has been developed forwelding metals and metal alloys. Friction stir welding is generally asolid state process. Solid state processing is defined herein as atemporary transformation into a plasticized state that typically doesnot include a liquid phase. However, it is noted that some embodimentsallow one or more elements to pass through a liquid phase, and stillobtain the benefits of the present invention.

The friction stir welding process often involves engaging the materialof two adjoining work pieces on either side of a joint by a rotatingstir pin. Force is exerted to urge the pin and the work pieces togetherand frictional heating caused by the interaction between the pin,shoulder and the work pieces results in plasticization of the materialon either side of the joint. The pin and shoulder combination or “FSWtip” is traversed along the joint, plasticizing material as it advances,and the plasticized material left in the wake of the advancing FSW tipcools to form a weld. The FSW tip can also be a tool without a pin sothat the shoulder is processing another material through FSP.

FIG. 1 is a perspective view of a tool being used for friction stirwelding that is characterized by a generally cylindrical tool 10 havinga shank 8, a shoulder 12 and a pin 14 extending outward from theshoulder. The pin 14 is rotated against a work piece 16 until sufficientheat is generated, at which point the pin of the tool is plunged intothe plasticized work piece material.

Typically, the pin 14 is plunged into the work piece 16 until reachingthe shoulder 12 which prevents further penetration into the work piece.The work piece 16 is often two sheets or plates of material that arebutted together at a joint line 18. In this example, the pin 14 isplunged into the work piece 16 at the joint line 18.

Referring to FIG. 1, the frictional heat caused by rotational motion ofthe pin 14 against the work piece material 16 causes the work piecematerial to soften without reaching a melting point. The tool 10 ismoved transversely along the joint line 18, thereby creating a weld asthe plasticized material flows around the pin from a leading edge to atrailing edge along a tool path 20. The result is a solid phase bond atthe joint line 18 along the tool path 20 that may be generallyindistinguishable from the work piece material 16, in contrast to thewelds produced when using conventional noon-FSW welding technologies.

It is observed that when the shoulder 12 contacts the surface of thework pieces, its rotation creates additional frictional heat thatplasticizes a larger cylindrical column of material around the insertedpin 14. The shoulder 12 provides a forging force that contains theupward metal flow caused by the tool pin 14.

During friction stir welding, the area to be welded and the tool aremoved relative to each other such that the tool traverses a desiredlength of the weld joint at a toolwork piece interface. The rotatingfriction stir welding tool 10 provides a continual hot working action,plasticizing metal within a narrow zone as it moves transversely alongthe base metal, while transporting metal from the leading edge of thepin 14 to its trailing edge. As the weld zone cools, there is typicallyno solidification as no liquid is created as the tool 10 passes. It isoften the case, but not always, that the resulting weld is adefect-free, re-crystallized, fine grain microstructure formed in thearea of the weld.

Travel speeds are typically 10 to 500 mm/min with rotation rates of 200to 2000 rpm. Temperatures reached are usually close to, but below,solidus temperatures. Friction stir welding parameters are a function ofa material's thermal properties, high temperature flow stress andpenetration depth.

Previous patents have taught the benefits of being able to performfriction stir welding with materials that were previously considered tobe functionally unweldable. Some of these materials are non-fusionweldable, or just difficult to weld at all. These materials include, forexample, metal matrix composites, ferrous alloys such as steel andstainless steel and non-ferrous materials. Another class of materialsthat were also able to take advantage of friction stir welding is thesuperalloys. Superalloys can be materials having a higher meltingtemperature bronze or aluminum, and may have other elements mixed in aswell. Some examples of superalloys are nickel, iron-nickel, andcobalt-based alloys generally used at temperatures above 1000 degrees F.Additional elements commonly found in superalloys include, but are notlimited to, chromium, molybdenum, tungsten, aluminum, titanium, niobium,tantalum, and rhenium.

It is noted that titanium is also a desirable material to use forfriction stir welding. Titanium is a non-ferrous material, but has ahigher melting point than other nonferrous materials. The previouspatents teach that a tool for friction stir welding of high temperaturematerials is made of a material or materials that have a higher meltingtemperature than the material being friction stir welded. In someembodiments, a superabrasive was used in the tool, sometimes as acoating.

Friction Stir Welding (FSW) has been in use now for almost 20 years as asolid state joining process. This process has evolved from being used onaluminum or low melting temperature materials to high meltingtemperature materials such as steel, stainless steel, nickel base alloysand others. Literature is replete with tool geometries and processparameters needed to have a repeatable process. An understanding of theFSW process is important to understanding the invention described below.

While FIG. 1 describes the general joining process, there is oneparticular problem that was not described. Once a friction stir weld orfriction stir processing pass is complete, the starting point of thejoint may be left with material flash caused by the initial tool plunge.In many applications, having material flash disposed on a work pieceafter FSW is unacceptable.

One method for removing material flash is a run-on tab. However, using arun-on tab may also lead to a requirement for additional fixturing, workpiece material, and post process removal methods. Furthermore, in manycases, a run-on tab is not an option because of space limitations, workpiece geometry, cost, etc.

An example of an application where a run-on tab may not be an optionwould be using FSW to repair certain cracks. For example, nuclearreactor containment vessels may not have the option for a run-on tab.Furthermore, the material flash that may be left over from the FSWplunge may create a new corrosion crack initiation site and cannot betolerated for safety reasons. There are many other examples of how aresulting FSW surface with material flash (hereinafter “flash”) may bedetrimental to product performance, safety, and cost.

In some cases, flash resulting from the plunge is not the onlydetrimental effect resulting from FSW. Other problems from FSW mayinclude unfavorable or detrimental residual stresses, tool undercut,flash along the weld due to tool wear or parameter selection, sharpflash locations creating safety concerns for human contact, inability tosee sub-surface defects, fatigue life compromised by surface anomaliesand others.

Having a consistent surface finish is preferred for engineeredcomponents in order to meet design and safety requirements. Thus, whatis needed is a way to join Advanced High Strength Steels (AHSS) that canbe used in the automotive and other industries.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system and methodfor modifying a work piece surface of high melting temperature materialssuch as Advanced High Strength Steels, wherein a friction stir weldingtool may include cutting elements located on the outside diameter of acollar assembly, wherein the collar assembly may be retrofitted forexisting friction stir welding tools, or may be designed as a customattachment for a new hybrid friction stir welding tool, wherein thesurface of the work piece may be modified by removing detrimental flashand burr created during operation of the friction stir welding tool.

These and other objects, features, advantages and alternative aspects ofthe present invention will become apparent to those skilled in the artfrom a consideration of the following detailed description taken incombination with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration of the prior art showing friction stir weldingof planar work pieces.

FIG. 2 is a perspective view of a friction stir welding tool that wasdesigned to accommodate cutting elements on an outside diameter orcollar of the tool.

FIG. 3 is a close-up view of the results of trying to remove a burrusing the friction stir welding tool of FIG. 2.

FIG. 4 is a perspective view of a floating outer collar for making ahybrid friction stir welding tool of the present invention.

FIG. 5 is a perspective view of the underside of the hybrid frictionstir welding tool showing a load pin adjustment used to set the heightof a cutting insert.

FIG. 6 is a cross sectional view of the hybrid friction stir weldingtool described in FIGS. 4 and 5.

FIG. 7 is a perspective view of a hybrid friction stir welding tool forremoving burrs and/or altering the surface of a work piece duringfriction stir welding.

FIG. 8 shows a uniformly machined surface of a stainless steel workpiece with a burr removed using a hybrid friction stir welding toolmodified to incorporate the present invention.

FIG. 9 is a perspective view of a collar assembly that may be used toretrofit an existing friction stir welding tool that already has acollar.

FIG. 10 is a hybrid friction stir welding tool that is a combination ofthe collar assembly of FIG. 9 and a friction stir welding tool that hasa collar.

FIG. 11 is a cross sectional view of the retrofitted friction stirwelding tool of FIG. 10.

FIG. 12 is a profile view of a hybrid friction stir welding toolincluding a peening surface modification tool.

FIG. 13 is a profile view of a hybrid friction stir welding toolincluding a grinding surface modification tool.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the drawings in which the various elementsof the present invention will be given numerical designations and inwhich the invention will be discussed so as to enable one skilled in theart to make and use the invention. It is to be understood that thefollowing description is only exemplary of the principles of the presentinvention, and should not be viewed as narrowing the claims whichfollow.

In a first embodiment shown in a perspective view in FIG. 2, the presentinvention shows a friction stir welding (hereinafter “FSW”) tool 30 thatmay be designed to accommodate at least one cutting element 32 on theoutside diameter or collar of the tool 30. Cutting elements 32 may belocated on the outside diameter of the FSW tool 30 as shown.

In this embodiment, three cutting elements 32 are disposed on theoutside diameter of the FSW tool 30. The cutting elements 32 areattached using a screw 34 as shown. Accordingly, the cutting elements 32may be replaced if worn or broken.

The number of cutting elements 32 is not limited to three, and may bedecreased to a single cutting element 32 or increased to as many asdesired. The cutting elements 32 may be replaceable. The FSW tool 30 maybe operated with or without the cutting elements 32. Accordingly, thecutting elements may or may not be a permanent fixture of the FSW tool30.

The cutting elements 30 may be a single material with a cutting edge, orit may be reinforced using additional materials or layers.

Experimental results using the FSW tool 30 of FIG. 2 demonstrate thatthe cutting elements 32 are effective in removing the detrimental flashand burr created during the plunging of the FSW tool 30.

FIG. 3 is a top view of a work piece 40 that has been friction stirwelded using the FSW tool 30 of FIG. 2. The work piece 40 shows theresults of FSW in stainless steel using the FSW tool 30 shown in FIG. 2,with three cutting elements 32. High machine loads were required forthis particular FSW geometry and an undesirable deflection of the FSWtool 30 created a natural tilt of a spindle (not shown) that wasrotating the FSW tool. This tilt, resulting from a “C Frame” style FSWmachine, caused the cutting elements 32 to cut only one side 44 of theprocessed FSW zone 42 as shown in FIG. 3. No cutting of the work piece40 occurred on the opposite side 46.

Undesirable deflection of the FSW tool 40 would not be a problem ifmachine loads were low, machine deflection was negligible, or the toolgeometry required lower loads. Accordingly, it was determined that thepresent invention needed further development to allow for FSW tool 30deflection which is typical during some FSW processes.

FIG. 4 shows a second embodiment of the present invention using a“floating” collar design to create a hybrid FSW tool. The hybrid FSWtool or floating collar design is comprised of an FSW tool 50, an innercollar 70 and a floating outer collar 58, wherein the FSW tool 50 mayinclude a shank 52, a shoulder 54 and a pin 56. The FSW tool 50 may ormay not include the pin 56. The floating outer collar 58 is disposedaround the inner collar 70 which is disposed around a top portion of theFSW tool 50.

The floating outer collar 58 may include two diametrically disposedrocker pins 60 that may give the floating outer collar 58 an additionaldegree of freedom, enabling the floating outer collar 58 to remain in aplaner position with respect to the surface of work piece 40 beingfriction stir welded or processed, while the FSW tool 50 and the innercollar 70 may be deflected to some degree with respect to the work piece40 while pivoting on the rocker pins 60.

In this second embodiment, a load pin 62 may remain in contact with asurface of the work piece 40 during FSW, which may offset the loadsapplied by a cutting insert 64. In the second embodiment, the threecutting elements 32 have been replaced by a single indexable cuttinginsert 64. The second embodiment may also include more than oneindexable cutting insert 64 disposed on the floating outer collar 58.

It should be understood that the FSW tool 50 may have many differentprofiles and still include some surface modification tool on thefloating outer collar 58. Accordingly, it is within the scope of theinvention that the FSW tool may have a shoulder 54 having any profilethat is known to those skilled in the art, including stepped, spiraled,concave, and convex or any other desirable profile. Regarding pins,there may be no pin on the shoulder, there may be a retractable pin or astandard pin. The pin may also have any pin profile that is desirablefor the particular application of the FSW tool.

FIG. 5 is a view of the underside of the floating outer collar 58 thatmay be disposed around the top portion of the FSW tool 50, and the innercollar 70. The height of the load pin 62 is adjusted using a cuttingheight adjustment screw 68 that is underneath the load pin 62. Thecutting height adjustment screw 68 may be an integral part of the loadpin or it may be separate. The height of the load pin 62 is adjustedprior to FSW. The load pin 62 is held in place using a set screw 66.

An outer surface of the inner collar 70 may be spherical to therebyenable continuous rocking or movement of the outer collar, about therocker pins 60. This concept of enabling the FSW tool 50 and the innercollar 70 to be able to move with respect to the floating outer collar58 in order to enable the floating outer collar to remain parallel to asurface of the work piece 40 enables the shank 52 of the FSW tool to beat a variable angle with respect to the surface of the work piece 40 atall times during FSW. In other words, the floating outer collar 58remains substantially parallel to the surface of a work piece while thefriction stir welding tool 50 and the inner collar 70 are free to moveand operate at an angle that is not perpendicular to the surface of thework piece.

FIG. 6 is a cross-sectional view of the second embodiment of the presentinvention. FIG. 6 shows the FSW tool 50 comprised of the pin 56, theshoulder 54, and the shank 52, and two collars comprised of the innercollar 70 and the floating outer collar 58 including the rocker pins 60(on opposite sides of the inner collar).

FIG. 7 is a perspective view of an FSW tool 50, inner collar 70 andfloating outer collar 58. The present invention therefore provides anFSW tool having a center geometry that performs FSW, along with an outergeometry that alters the surface of the work piece material beingprocessed.

FIG. 8 shows a uniformly machined surface of a stainless steel workpiece 40. A burr was removed using the FSW tool 50, the inner collar 70and the floating outer collar 58 of the present invention.

FIG. 9 is a perspective view of an inner collar 70 and the floatingouter collar 58 in a third embodiment that can be coupled to an existingFSW tool (not shown) having a collar. Also shown are the rocker pins 60on opposite sides of the collars 58, 70, as well as the set screw 66 theload pin 62 and the indexable cutting insert 64. This collar assembly 72can be coupled to an existing FSW tool as a retrofit in order to takeadvantage of the principles of the present invention.

FIG. 10 is a perspective view of the collar assembly 72 of FIG. 9 thatis now coupled to an existing FSW tool 74. The FSW tool 74 has its ownstandard collar 80, but is now adapted to be coupled to the collarassembly 72. An adapter collar 82 is coupled to the standard collar 80using a method that is known to those skilled in the art. The adaptercollar 82 may include a lip lock 84 on which the inner collar 70 canrest.

It should be understood that any appropriate means can also be used forattaching the collar assembly 72 to the FSW tool 74.

FIG. 11 is a cross-sectional view of the embodiment of FIG. 10, showingretaining lip lock 84 to maintain cutter location during FSW.

FIGS. 2-11 above illustrate the concept of creating a hybrid FSW toolthat not only friction stir welds or processes a given work piece, butalso machines the surface of the work piece at the same time in order tocreate the desired surface finish.

The present invention can be further modified by attaching other surfacemodification tools to the floating outer collar 58 to alter the surfaceof the work piece according to the designer's design parameters. Inother words, in place of the indexable cutting insert 64, a differenttool may be attached to the floating outer collar 58.

FIG. 12 is a profile view of another hybrid friction stir welding tool90 of the present invention. In this simplified diagram, an FSW tool 50has an inner collar 70 and a floating outer collar 58. FIG. 12 is beingshown to illustrate a surface modification tool other than an indexablecutting insert 64. However, instead of being placed in the same locationas the insert, the surface modification tool is disposed in a surface 92of the floating outer collar 58. In this figure, at least one elongatedball 94 is disposed in the surface 92. The ball 94 may be held rigidlyin the surface 92, or it may be free to rotate. The ball 94 is providedfor peening or burnishing of the work piece. A plurality of balls 94 mayalso be disposed in the surface 92. The balls 94 may be elongated orround.

FIG. 13 is a profile view of another hybrid friction stir welding tool100 of the present invention. In this simplified diagram, an FSW tool 50has an inner collar 70 and a floating outer collar 58. FIG. 13 is beingshown to illustrate a surface modification tool other than an indexablecutting insert 64. However, instead of being placed in the same locationas the insert, the surface modification tool is disposed in the surface92 of the floating outer collar 58. In this example, at least one wheel102 is shown disposed in the surface of the floating outer collar 58.The wheel 102 may be a grinding wheel. The wheel 102 may be replaceablein order to use a wheel having different profiles or materials on thewheel, such as a grit for a grinding wheel. The wheel 102 may usebearings or a pin to enable rotation of the wheel.

Possible surface modification tools include but should not be consideredto be limited to a rolling ball that may or may not be located where theindexable cutting insert 64 is now located, the rolling ball being usedto create a shot peened surface to create residual compressive stresses,and thereby increasing fatigue life of the work piece. In anotherembodiment, a stationary ball or ball-like geometry may also be mountedin order to burnish the work piece surface to improve surface finish,reduce corrosion potential and/or improve fatigue properties. In anotheralternative embodiment, a mirror may also be mounted to provide areflective surface so that continuous laser processing of the work piecesurface may be achieved to alter or reduce surface residual stresses, orlaser process the surface of the friction stir processed zone. Formaterials that harden during the friction stir process, in anotheralternative embodiment, a grinding fixture may be used to alter the workpiece surface as well.

The FSW tools described above will have at least one cutting element orother surface modifying tool, but may contain more. The FSW tool mayhave at least one grinding element or feature, at least one burnishingelement or feature, at least one peening element or feature, at leastone reflective element or feature for laser transmission. In analternative embodiment, the FSW tool may have more than one feature on afloating outer collar 58.

The FSW tool may have a rotational speed between 10 and 40200 RPM, andcan apply loads between 50 lbf and 60,000 lbf along an FSW tool axis.The FSW tool may use an alternate heating source around the FSW toolusing inductive, resistive, IR, or other methods known to the FSWindustry. The heating source will affect the characteristics of theresulting weld formed by FSW.

In another alternative embodiment, the FSW tool may use an alternatecooling source around the FSW tool to thereby affect the operatingcharacteristics of the FSW tool. In another alternative embodiment, theFSW tool may have a detachable/modular surface modification tool, or anintegrated surface modification tool. The FSW tool may contain any ofthe metals outlined in the periodic table. The FSW tool may be operatedwhen surrounded by a liquid or fluid, and be used with a shielding gasor operated in air.

The FSW tool may be used to process those materials found in columns 1Athrough 7A on the Periodic Table and all transition elements andcombinations of these elements.

The FSW tool may be modular, or in other words, it may have replaceablecomponents and features that can be attached for modifying a work piecesurface. The FSW tool may be used in conjunction with a surfacemodification tool used on a separate spindle or device. The FSW tool mayhave a retractable pin, or be used with a bobbin tool design. The FSWtool may also have a shoulder and pin that are controlled independentlyof the surface modification tool. The FSW tool may operate wherein thesurface modification tool operates at different speeds from the frictionstirring tool element. The FSW tool may also be operated in atemperature control mode.

The surface modification tool that may be coupled to the FSW tool may beany consumable.

The FSW tool may be operated as a spot welding tool with no translationmotion.

The FSW tool may have a friction element that is consumable (i.e.friction hydropillar).

The FSW tool may be operated wherein no friction element serves as aclamping device. The FSW tool may be used on a non-planer surface.

The work pieces may have another material or greater material thicknessthan the parent material to allow for stock removal or modification ifneeded.

Without departing from the scope of this invention, in anotheralternative embodiment, one or more other spindles may be attached to amachine that is holding and rotating a first FSW tool. It may bepossible to allow the FSW process to occur during a same pass, whileallowing for different surface speeds to be achieved by using thedifferent spindle heads. Thus, the second spindle head may be movablerelative to the position of the first spindle head in order to performFSW at some location near to the first spindle head. But not always inthe same location relative to the first spindle head.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention. The appended claims are intended tocover such modifications and arrangements.

What is claimed is:
 1. A system for removing surface features on a workpiece during friction stir welding, the system comprising: a frictionstir welding tool having a shank, a shoulder, and an inner collardisposed around the shoulder near a working end of the friction stirwelding tool, the friction stir welding tool being configured to rotateabout a longitudinal axis extending therethrough; a floating outercollar rotationally fixed about the longitudinal axis relative to theinner collar and movably coupled to the inner collar about a lateralrotational axis, the lateral rotational axis being transverse to thelongitudinal axis; and at least one insert connected to a surface of thefloating outer collar.
 2. The system of claim 1, the lateral rotationalaxis being perpendicular to the longitudinal axis.
 3. The system ofclaim 1, the floating outer collar being movably coupled to the innercollar by one or more rocker pins positioned radially through thefloating outer collar and the inner collar, the one or more rocker pinsdefining the lateral rotational axis.
 4. The system of claim 1, the atleast one insert being a cutting insert.
 5. The system of claim 1, theat least one insert being a surface modifying tool, wherein the surfacemodifying tool is a grinding element, a burnishing element, a peeningelement, or a reflective element.
 6. The system of claim 1, a positionof the at least one insert being adjustable relative to the surface ofthe floating outer collar.
 7. The system of claim 1, further comprisingat least one load pin connected to the surface of the floating outercollar and configured to offset a torque applied to the floating outercollar by the at least one insert when in contact with the work piece.8. The system of claim 7, a position of the at least one load pin beingadjustable relative to the surface of the floating outer collar.
 9. Thesystem of claim 1, the at least one insert comprising a plurality ofcutting inserts.
 10. A system for removing surface features on a workpiece during friction stir welding, the system comprising: a frictionstir welding tool having a shank, a shoulder, and an inner collardisposed around the shoulder near a working end of the friction stirwelding tool, the friction stir welding tool being configured to rotateabout a longitudinal axis extending therethrough; a floating outercollar located circumferentially about the inner collar and rotationallyfixed about the longitudinal axis relative to the inner collar, thefloating outer collar being movably coupled to the inner collar about alateral axis of rotation through the inner collar, the lateral axis ofrotation being transverse to the longitudinal axis; and at least oneinsert disposed on the floating outer collar.
 11. The system of claim10, the friction stir welding tool further comprising an adapter collarpositioned between the inner collar and the shoulder.
 12. The system ofclaim 10, the at least one insert comprising a cutting insert and asurface modifying tool, the cutting insert and surface modifying toolbeing each configured to offset torque applied to the floating outercollar by the other.
 13. The system of claim 10 further comprising acooling element in thermal communication with the friction stir weldingtool.
 14. The system of claim 10 further comprising a heating elementconfigured to apply thermal energy to the work piece.
 15. The system ofclaim 10, the floating outer collar being coupled to the inner collar byone or more rotatable pins, the rotatable pins being configured totransmit up to 60,000 pound-feet of torque to the at least one insert.16. The system of claim 10, the at least one insert being rotatablerelative to a surface of the floating outer collar.
 17. A system forremoving surface features on a work piece during friction stir welding,the system comprising: a friction stir welding tool having a shank, ashoulder, an axis of rotation, and an inner collar disposed around theshoulder near a working end of the tool; a floating outer collar movablycoupled to the inner collar by one or more rocker pins inserted throughthe floating inner collar and at least partially through the innercollar, the floating outer collar having a working surface in thedirection of the working end of the friction stir welding tool; and atleast one cutting insert disposed on the floating outer collar, at leastpart of the cutting insert extending a cutting distance beyond theworking surface in the direction of the working end of the friction stirwelding tool.
 18. The system of claim 17 further comprising a secondinsert disposed on the floating outer collar, the at least one cuttinginsert being disposed a first radius from the axis of rotation and thesecond insert being disposed a second radius from the axis of rotation.19. The system of claim 18, the first radius and the second radius beingdifferent.
 20. The system of claim 17, the at least one cutting insertbeing adjustable to alter the cutting distance.